Spur pump gear systems generally consist of two or more spur gears operating in mesh. The gear set operates in a sealed housing with the drive gear turning the driven gear in mesh at drive top dead bend. The bottom dead bend is generally sealed with the tips of the gear teeth as they turn in the housing pocket.
Conventional spur gear pumps utilize involute gear forms which are well suited to most applications.
For example U.S. Pat. No. 246,724 illustrates a pair of spur gears.
Furthermore U.S. Pat. No. 3,130,682 teaches a gear pump comprising a housing having and inlet and an outlet port and a pair of meshing gears rotatably received in the housing, the gears each having involute gear teeth forming a deddendum pocket therebetween in the areas of meshing engagement.
Yet another arrangement is shown in U.S. Pat. No. 2,975,718 which illustrates two meshing spur gears which are journalled on stub shafts.
Finally, U.S. Pat. No. 294,026 teaches pistons made with a series of thin curved wings or blades extending outwardly in a radial manner from the central hob or core.
In some cases where the size of the gear housing is restricted, and a large flow of oil is required from the pump, gears with as few as seven teeth are used to produce the maximum flow volume from the pump. Due to the mathematical generation of involute curves, the gear teeth in such situations will tend to push the limitations of the involute form causing the gear set to operate with contact ratios only slightly higher than 1.0 and producing high contact stresses in the root area of the gear.
Accordingly, it is an object of this invention to produce an improved spur gear set and in particular to provide an improved spur gear pump system.
It is an aspect of this invention to provide a spur gear set comprising; a drive spur gear journalled for rotation about a first axis, said drive gear presenting epi and hypo cycloid tooth profiles; a driven spur gear journalled for rotation about a second axis, said driven spur gear presenting epi and hypo cycloid tooth profiles; said epi cycloid tooth profile of said driven spur gear engagedly driving said hypo cycloid tooth profile of said driven spur gear.
It is another aspect of this invention to provide a spur pump gear system comprising; a housing having a sealed chamber communicating with an intake port and a discharge port; a shaft journalled for rotation within said chamber; a drive spur gear mounted concentrically on said shaft for rotation about a first axis within said chamber, said drive spur gear presenting epi and hypo cycloid tooth profiles; a driven spur gear disposed internally within said chamber for rotation about a second axis, said driven spur gear presenting epi and hypo cycloid tooth profiles; said epi cycloid tooth profile of said drive spur gear engagedly driving said hypo cycloid tooth profile of said driven spur gear.
It is another aspect of this invention to provide a method of producing cycloid tooth profiles for a spur gear set comprising the steps of; determining the outside diameter of a first spur gear; generating a pitch circle of said first spur gear; producing an epi cycloid by rolling said epi cycloid in a clockwise direction about said pitch circle of said first spur gear starting at the vertical axis until said epi cycloid intersects said outside diameter of said first spur gear; producing a hypo cycloid by rolling said hypo cycloid in a counterclockwise direction around said pitch circle of said first spur gear starting at the vertical axis until said generated curve intersects the tooth flank of said first spur gear; connecting said epi and hypo cycloid to the profiles of said first spur gear; completing the tooth profile of said first spur gear by rotating and mirroring the resulting gear form about said pitch circle of said first spur gear at increments equal to 360 divided by the number of teeth of said first spur gear; repeating the above steps for said second spur gear.